That's really an impossible question to answer, but the amount of rake you pay often comes as a surprise. How much you pay depends (of course) on the stakes and number of hands you play, as well as your style and the type of games and tables you play.
You can check the rake you paid in indvidual sessions and/or hands if you think there is anything unusual, but I'm not aware of any problems with rake at Full Tilt (and we have a lot of Full Tilt players so issues like that normally come up pretty quickly).
You may be able to find a "typical" amount of rake to be paying for your game type somewhere like the strategy forums on 2+2.